Question 892518
let f = father's present age
let s = son's age
:
write an equation for each statement, simplify as much as possible.
:
 Five years ago a father was thrice as old as his son.
f - 5 = 3(s-5)
f - 5 = 3s - 15
f = 3s - 15 + 5
f = 3s - 10
:
 Fifteen years hence he will be twice as old as his son find the present age of his son (in years)
f + 15 = 2(s + 15)
f + 15 = 2s + 30
f = 2s + 30 - 15
f = 2s + 15
:
f=f, therefore
3s - 10 = 2s + 15
3s - 2s = 15 + 10
s = 25 yrs is the son's age
:
:
You can check this yourself, find the father's age and check both statements